Network Working Group B. Foster
Request for Comments: 3064 Cisco Systems
Category: Informational February 2001
MGCP CAS Packages
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
This document contains a collection of media gateway Channel
Associated Signaling (CAS) packages for R1 CAS, North American CAS,
CAS PBX interconnect as well as basic FXO support. Included are six
packages. The "MS" package covers MF single stage dialing trunks.
This includes wink start and immediate start PBX DID/DOD trunks as
well as basic R1 and Feature Group D (FGD) Terminating protocol [3].
The "DT "package covers immediate start and basic DTMF and dial-pulse
trunks and the "BL" package covers the interface to a basic PBX
(digital or FXS interface). In addition to the Terminating protocol,
there are three other FGD protocols described in [3]. These include
EAIN and EANA which is covered by the enclosed "MD" package and the
Operator Service Signaling protocol which is handled by the "MO"
package. Support for basic FXO interconnect is provided by "DO"
package.
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119.
IESG Note:
This document is being published for the information of the
community. It describes a protocol that is currently being deployed
in a number of products. Implementers should be aware of
developments in the IETF Megaco Working Group and ITU SG16 who are
currently working on a potential successor to this protocol.
Table of Contents
1.0.Introduction ................................................ 3
1.1. Functional Partitioning .................................... 3
1.2. CAS Trunk Types ............................................ 4
1.2.1. "MS" Package ............................................. 5
1.2.2. "DT" Package ............................................. 5
1.2.3. "BL" Package ............................................. 6
1.2.4. "DO" Package ............................................. 6
1.2.5. "MD" Package ............................................. 6
1.2.6. "MO" Package ............................................. 7
2.0. Event Packages ............................................. 7
2.1. Events and Signals for the "MS" package .................... 9
2.2. Events and Signals for the "DT" package .................... 10
2.3. Events and Signals for the "BL" package (Basic PBX) ........ 10
2.4. Events and Signals for the "DO" package .................... 11
2.5. Events and Signals for the "MD" package .................... 12
2.6. Events and Signals for the "MO" package .................... 13
2.7. Event and Signal Descriptions .............................. 13
3.0. Hook-State Signals and Events .............................. 23
3.1. Overview of Approach ....................................... 23
3.2. Suspend/Resume Processing .................................. 23
3.3. Control over Disconnect for E911 ........................... 24
3.3. Release and Release Complete ............................... 24
3.4. Blocking CAS Trunks ........................................ 26
3.5. Summary of Hook-State Events ............................... 26
4.0. Glare Handling ............................................. 27
4.1. Glare on MF Bi-directional Wink-start Trunks ............... 27
4.2. Glare Handling - Basic PBX Trunks .......................... 27
5.0. Example Call Flows ......................................... 28
5.1. PBX to PBX ("MS", "DT, and "BL" packages)................... 28
5.1.1. Call Setup Flows ......................................... 28
5.1.2. Call Tear-Down ........................................... 34
5.1.2.1. Origination End Initiates the Release .................. 35
5.1.2.2. Termination End Initiates the Release .................. 38
5.2. Example Call Flows - "DO" package .......................... 40
5.2.1. Call Setup Flows ......................................... 40
5.2.2. Call Tear-Down ........................................... 42
5.3. Example Call Setup - "MD" Package .......................... 44
5.4. Example Call Setup - "MO" Package .......................... 51
Acknowledgements ................................................ 54
References ...................................................... 55
Author's Address ................................................ 55
Full Copyright Statement ........................................ 56
1.0.Introduction
1.1. Functional Partitioning
There are a number of different possible approaches for partitioning
the functional responsibility between the Call Agent and the Media
Gateway:
* The Call Agent takes all of the responsibility for the CAS state
machine giving the media gateway detailed commands
* The media gateway contains the CAS state machine and provides an
abstract interface to the Call Agent
Timing requirements of CAS protocols often involve reacting within
time intervals measured in tens of milliseconds which makes direct
control of timing impossible. The approach used here is to allow the
media gateway to handle low level CAS protocol and timing details
where at all possible and have the Call Agent involved only whenever
higher level processing is required.
Taking this approach, the ideal situation would be to allow the Call
Agent to treat as many CAS protocols in a similar way, leaving the
details to the media gateway. Example: for an incoming MF trunk that
involves a single incoming digit string, the Call Agent should not
care whether this is a wink start trunk or an immediate start trunk
(media gateway should not have to provide the wink-start signal).
Some goals in partitioning responsibility between the media gateway
and media gateway:
* Minimize the number of interactions between the Call Agent and the
media gateway.
* The media gateway should not have to do digit analysis (e.g., to
determine that the incoming digits contain carrier access
information). This is a Call Agent's responsibility.
* Provide some reasonable level of abstraction for the Call Agent so
that it can reuse call flows when possible (e.g., Call Agent
should not have to differentiate between wink start and immediate
start interfaces when only one digit string is involved).
* The media gateway should take care of the CAS protocol (and
timeouts) where possible with the Call Agent taking over
responsibility where the media gateway leaves off.
Use of Embedded Notifications: Rather than depending on the use of
embedded notifications, signals and events were defined that had the
specific semantics required. There are two reasons for this:
a) It allows an abstract interface for the Call Agent so that for
example, the same incoming call-setup event can be used in the case
of MF wink start and MF immediate start trunks, presenting a common
interface to the Call Agent even though the semantics at the CAS
state-machine level are slightly different (i.e., in the MF wink
start case, a wink-start signal is provided reflexively as a result
of an incoming seizure, where as in the immediate start case, this is
not required).
b) Potential events that might trigger an embedded notification
(e.g., the incoming seizure mentioned above) typically needed to be
visible to the Call Agent for billing anyway.
This does not say that embedded notifications cannot be used. It
simply does not necessitate their use.
Out-pulsing Approach: In order to provide the semantics for
outpulsing, special higher level signals (e.g., "sup" for call set-up
and "inf" for information) are included that contain the necessary
semantics.
Off-hook and On-hook Signals and Events: A higher level view of off-
hook and on-hook events is taken in order to make the interface
Q.931-like. This provides the advantage that:
* Similar call flows result when dealing with Q.931-based interfaces
(e.g., PRI)
* It's more evident (for ease in debug) when looking at message as
to exactly what is going on without having to refer to previous
events
1.2. CAS Trunk Types
The following describes the types of trunks supported by the various
packages. Configuration of the specific trunk type (e.g., wink start
versus immediate start) is done within the Media Gateway (MG) via
provisioning facilities outside the scope of MGCP. The Call Agent's
responsibility is to support the particular package (i.e., in general
the Call Agent does not have to differentiate between wink start and
immediate start, since those differences are taken care of by the
MG). However, the Call Agent needs to know which trunks are
incoming, outgoing or bi-directional.
1.2.1. "MS" Package
The "MS" package is used for PBX DID/DOD trunks as indicated in the
following table. It is also used for incoming or outgoing MF wink
start trunks (R1 and FGD Terminating protocol [6]).
Table 1 MF PBX Trunks
--------------------------------------------------
| Trunk Type | Direction (w.r.t. the gateway) |
--------------------------------------------------
|MF, wink start |Incoming - originate from PBX |
| |(the same as FGD terminating |
| | protocol) |
|MF, wink start |Outgoing - terminate on PBX |
|MF, wink start |Bi-directional |
|MF, Immediate |Incoming (originate from PBX) |
| start | |
|MF, Immediate |Outgoing (terminate on PBX) |
| start | |
--------------------------------------------------
1.2.2. "DT" Package
DTMF and dial-pulse (DP) trunks (except basic PBX) are covered by the
"DT" package along with the DTMF "D" package:
Table 2 DTMF and DP Wink Start and Immediate Start Trunks
--------------------------------------------------
| Trunk Type | Direction (w.r.t. the gateway) |
--------------------------------------------------
|DTMF, Immediate |Incoming (originate from PBX) |
| start, wink | |
| start | |
|DTMF, Immediate |Outgoing (terminate on PBX) |
| start, wink | |
| start | |
--------------------------------------------------
1.2.3. "BL" Package
DTMF and dial-pulse (DP) basic PBX trunks are covered by the "BL"
package - along with the DTMF "D" package (essentially this is like a
"basic line with no features") - either digital or FXS trunk
interface:
Table 3 Basic FXS Interface
--------------------------------------
| Trunk Type | Direction |
| | (w.r.t. the gateway) |
--------------------------------------
|Basic, DTMF and |Bi-directional |
|DP, Loop Start | |
|Basic, DTMF and |Bi-directional |
|DP, Ground Start| |
--------------------------------------
1.2.4. "DO" Package
The "DO" package is used for analog FXO loop-start and ground-start
analog trunks as indicated in the following table.
Table 4 FXO analog PBX Trunks
--------------------------------------
| Trunk Type | Direction |
| | (w.r.t. the gateway) |
--------------------------------------
|FXO, loop-start|Bi-directional |
|FXO, ground- |Bi-directional |
| start | |
--------------------------------------
1.2.5. "MD" Package
The MD package provides support for North American MF Feature Group D
EANA and EAIN [3], allowing the Media Gateway to be at either the end
office, the carrier or the tandem side of the circuit. The CAS
Signaling Type column of the following tables is intended to indicate
signaling differences that are of common interest to both the Call
Agent and Media Gateway. Configuration information that is only of
interest to the Media Gateway is not identified.
Table 4 Feature Group D MF Trunks Supported
--------------------------------------------------
| Trunk Type | Direction (w.r.t. the gateway) |
--------------------------------------------------
|FGD, EANA |Outgoing (End Office to Carrier) |
|FGD, EANA |Incoming (Carrier to End Office) |
|FGD, EAIN |Outgoing (End Office to Carrier) |
|FGD, EAIN |Incoming (Carrier to End Office) |
--------------------------------------------------
Note that EANA and EAIN signaling may be requested on the same trunk
on a call-by-call basis.
1.2.6. "MO" Package
The "MO" package is used for FGD Operator Services Signaling,
outgoing trunks only. Feature Group C can also be supported by the
same interface.
2.0. Event Packages
This section defines the event packages. The terms "signal" and
"event" are used to differentiate a command from a Call Agent to a
Media Gateway ("signal") from an "event" that is detected by the
Media Gateway and then is "Notified" to the Call Agent.
Each package definition includes a package name, plus the event name
codes and the definitions for each of the events in the package. In
the tables of events/signals for each package, there are five
columns:
* Code The package unique event code used for the
event/signal.
* Description A short description of the event/signal.
* Event An "x" appears in this column if the event can be
Requested by the Call Agent. Alternatively, one or
more of the following symbols may appear:
- "P" indicating that the event is persistent,
- "S" indicating that the event is an event-state that may be
audited,
- "C" indicating that the event/signal may be detected/applied
on a connection. If "C" is associated with an event, this
refers to an event that can occur on the media stream.
However, "C" may also be associated with a signal (in the
signal column), the signal can be requested to sent over a
connection.
Note that the intent of being able to audit state ("S") in an event
in the following packages is to answer one of the two questions:
1. Has a call been initiated on this line/trunk? For example in
the packages that follow, call setup initiation is indicated by
either a "sup" event or an "hd" (FXS - "BL" packages) or in the
case of the "DO" package below (FXO), by the "rg" event so that
those events have an "S" in the event column indicating that they
are auditable.
2. The other question of interest is to know whether the telephony
leg of the call is in the idle state so that a new call can be
initiated. This is indicate by the "rlc" (release complete)
event-state for packages that have that event.
* Signal If nothing appears in this column then this event
cannot be signaled on request by the Call Agent.
Otherwise, one of the following symbols is provided
to identify the type of signal:
- "OO" On/Off signal. The signal is turned on until commanded
by the Call Agent to turn it off, and vice versa.
- "TO" Timeout signal. The signal lasts for a given duration
unless it is superseded by a new signal or terminated on
detection of an event. Default time-out values are
supplied. A value of zero indicates that the time-out
period is infinite. The provisioning process may alter
these default values.
- "BR" Brief signal. The signal has a short, known duration.
* Additional info Provides additional information about the
event/signal, e.g., the default duration of TO signals.
Unless otherwise stated, all of the events/signals are
detected/applied on endpoints and audio generated by them is not
forwarded on any connection the endpoint may have. Audio generated
by events/signals that are detected/applied on a connection will
however be forwarded on the associated connection irrespective of the
connection mode.
2.1. Events and Signals for the "MS" package:
The following codes are used to identify events and signals for the
"MS" package:
Table 5 "MS" Package Events and Signals
---------------------------------------------------------------------
|Code|Description |Event|Signal |Additional Info |
|---------------------------------------------------------------------|
|ans |Call Answer | P | BR | |
| bl |Block | S | BR | |
| bz |Busy tone | - | TO |Time-out = 30 seconds |
|inf |Information Digits| x | - | |
| oc |Operation Complete| x | - | |
| of |Operation Fail | x | - | |
|rel |Release Call | P | BR | |
|res |Resume call | P | BR | |
|rlc |Release complete | P,S | BR | |
| ro |Reorder tone | - | TO |Time-out = 30 seconds |
| rt |Ringback tone | - | TO |Time-out = 180 seconds |
|sup |Call Setup | P,S | TO |Time-out when signal completes |
| | | | |out-pulsing |
|sus |Suspend call | P | BR | |
---------------------------------------------------------------------
2.2. Events and Signals for the "DT" package:
The following codes are used to identify events and signals for the
"DT" package:
Table 6 "DT" Package Events and Signals
---------------------------------------------------------------------
|Code|Description |Event|Signal |Additional Info |
|---------------------------------------------------------------------|
|ans |Call Answer | P | BR | |
| bl |Block | S | BR | |
| bz |Busy tone | - | TO |Time-out = 30 seconds |
| dl |Dial tone | - | TO |Time-out = 16 seconds |
| oc |Operation Complete| x | - | |
| of |Operation Fail | x | - | |
|rel |Release Call | P | BR | |
|res |Resume call | P | BR | |
|rlc |Release complete | P,S | BR | |
| ro |Reorder tone | - | TO |Time-out = 30 seconds |
| rt |Ringback tone | - | TO |Time-out = 180 seconds |
|sup |Call Setup | P,S | TO |Time-out when signals completed|
| | | | |out-pulsing |
|sus |Suspend call | P | BR | |
---------------------------------------------------------------------
2.3. Events and Signals for the "BL" package (Basic PBX)
The following codes are used to identify events and signals for the
"BL" package. This package looks very much like a simplified line
package:
Table 7 "BL" Package Events and Signals
---------------------------------------------------------------------
|Code|Description |Event|Signal |Additional Info |
|---------------------------------------------------------------------|
| bz |Busy tone | - | TO |Time-out = 30 seconds |
| dl |Dial tone | - | TO |Time-out = 16 seconds |
| hd |Off-hook | P,S | - | |
| hf |Flash hook | P | - | |
| hu |On-hook | P,S | - | |
| oc |Operation Complete| x | - | |
| of |Operation Fail | x | - | |
| rel|Release | - | BR | |
| rg |Ringing | - | TO |Time-out = 180 seconds |
| ro |Reorder tone | - | TO |Time-out = 30 seconds |
| rt |Ringback tone | - | C,TO |Time-out = 180 seconds |
---------------------------------------------------------------------
2.4. Events and Signals for the "DO" package:
The following codes are used to identify events and signals for the
"DO" package:
Table 8 "DO" Package Events and Signals
---------------------------------------------------------------------
|Code|Description |Event|Signal |Additional Info |
|---------------------------------------------------------------------|
| ci |Caller id | x | - | |
| hd |Offhook | - | BR | |
| hf |Hook flash | - | BR | |
| hu |Onhook | - | BR | |
| oc |Operation Complete| x | - | |
| of |Operation Fail | x | - | |
|rel |Release call | P | - | |
| rg |Ringing | P,S | - | |
|rlc |Release complete | P,S | - | |
|sup |Call Setup | - | TO |Time-out when signal completes |
| | | | | out-pulsing |
---------------------------------------------------------------------
2.5. Events and Signals for the "MD" package:
The following codes are used to identify events and signals for the
"MD" package.
Table 9 "MD" Package Events and Signals
---------------------------------------------------------------------
|Code|Description |Event|Signal |Additional Info |
|---------------------------------------------------------------------|
|ans |Call Answer | P | BR | |
|awk |Acknowledge wink | P | BR | |
| bl |Call Block | S | BR | |
| bz |Busy tone | - | TO |Time-out = 30 seconds |
|cwk |Continue Wink | - | BR | |
|inf |Information Digits| x | TO |Time-out when signals completed|
| | | | | out-pulsing |
| oc |Operation Complete| x | - | |
| of |Operation Fail | x | - | |
|rel |Release Call | P | BR | |
|res |Resume call | P | BR | |
|rlc |Release complete | P,S | BR | |
| ro |Reorder tone | - | TO |Time-out = 30 seconds |
| rt |Ringback tone | - | TO |Time-out = 180 seconds |
|sup |Call Setup | P,S | TO |Time-out when signals completed|
| | | | | out-pulsing |
|sus |Suspend call | P | BR | |
|swk |Start Wink | x | - | |
---------------------------------------------------------------------
2.6. Events and Signals for the "MO" package:
The following codes are used to identify events and signals for the
"MO" package.
Table 10 "MO" Package Events and Signals
---------------------------------------------------------------------
|Code|Description |Event|Signal |Additional Info |
|---------------------------------------------------------------------|
|ans |Call Answer !Note | P | - | |
| oc |Operation Complete| x | - | |
| of |Operation Fail | x | - | |
|orbk|Operator Ringback | x | - | |
|rbz |Reverse make busy | P,S | - | |
|rcl |Operator Recall | - | BR | |
|rel |Release Call | P | BR | |
|res |Resume Call | - | BR | |
|rlc |Release complete | P,S | BR | |
|sup |Call Setup | - | TO | |
|sus |Suspend Call | - | BR | |
|swk |Start Wink | x | - | |
---------------------------------------------------------------------
!Note: There is no indication that the operator answered the call.
The "ans" event is an indication that off-hook was received
from the far end which simply indicates that the destination
address was received properly and the calling number is in the
process of being outpulsed.
2.7. Event and Signal Descriptions
The following provides a list of the event and signal descriptions.
The event/signal name appears in parenthesis followed by the
corresponding Event + Signal attribute code plus a list of the
packages in which the event/signal occurs.
Call answer (ans; P + BR; DT,MD,MS,MO): Off-hook signal normally
indicates that the call has been answered and that cut-through has
been established. The exception is the "MO" package where it simply
indicates that off-hook was received and the calling number is in the
process of being sent (i.e., there is no event available to indicate
that the operator answered the call for operator services signaling).
Acknowledgement Wink (awk; P + BR; MD): This event is only applicable
to the "md" package. It provides an indication that all digits have
been received correctly. In an outgoing trunk, the event is
requested and when received indicates that the connecting switch
received all of the addressing information. On an originating trunk,
this signal is sent to inform the other end that all addressing
information has been received. If the Call Agent is providing a
transit application for example, in which incoming and outgoing
trunks are both EANA trunks, then after acknowledgement wink is
received from the terminating trunk, it is passed to the originating
side so that the originating side knows that addressing has passed to
the destination switch.
Call Block (bl; S + BR; DT,MS,MD): A steady off-hook signal applied
to one-way incoming trunks to indicate that no further calls will be
accepted. When "bl" is used as a signal then the "rel" signal is
used to release the blocking condition.
A Call Agent should only request the "bl" event in a case where it
knows that this is a one-way outgoing trunk, and it should never see
an incoming call-setup request ("sup" event). As such if "bl" is
requested as an event, then "sup" is suppressed as a persistent
event.
Busy tone (bz ; - + TO; BL,DT,MD,MS): Refer to ITU E.180. The
definition of the tone is defined by the national characteristics and
may be established via provisioning. Station Busy is defined in GR-
506-CORE - LSSGR, SIGNALING, Section 17.2.6. as a combination of two
AC tones with frequencies of 480 and 620 Hertz and levels of -24 dBm
each, to give a combined level of -21 dBm. The cadence for Station
Busy Tone is 0.5 seconds on followed by 0.5 seconds off, repeating.
Caller Id (ci(time, number, name); x + -; DO): See TR-NWT-001188,
GR-30-CORE, and TR-NWT-000031. Each of the three fields are
optional, however each of the commas will always be included.
The time parameter is coded as "MM/DD/HH/MM", where MM is a two-
digit value for Month between 01 and 12, DD is a two-digit value
for Day between 1 and 31, and Hour and Minute are two-digit values
coded according to military local time, e.g., 00 is midnight, 01
is 1 a.m., and 13 is 1 p.m.
The number parameter is coded as an ASCII character string of
decimal digits that identify the calling line number. White
spaces are permitted if the string is quoted, however they
will be ignored.
The name parameter is coded as a string of ASCII characters that
identify the calling line name. White spaces are permitted if the
string is quoted.
A "P" in the number or name field is used to indicate a private
number or name, and an "O" is used to indicate an unavailable number
or name. The following example illustrates the use of the caller-id
event:
O: ci(10/14/17/26, "555 1212", somename)
Continue Wink (cwk ; - + BR; MD): This signal is only applicable to
the "md" package. It provides an indication that digits sent have
been accepted, and further digits must be sent in order to process
the call. For example, when using FGD EAIN signaling, this would
correspond to sending a wink after the country access code had been
received to indicate readiness to receive identification and address
fields.
Dial-tone (dl ; - + TO; BL,DT): Refer to ITU E.180. The definition
of the tone is defined by the national characteristics and may be
established via provisioning. In GR-506-CORE - LSSGR, SIGNALING,
Section 17.2.1, sial Tone is defined as a combination of two
continuous AC tones with frequencies of 350 and 440 Hertz and levels
of -13dBm each to give a combined level of -10 dBm. It is considered
an error to try and play dial-tone on a phone that is on hook and an
error should consequently be returned when such attempts are made
(error code 402 - phone on hook).
Information Digits (inf(<inf-digits>); x + TO; MS,MD): On an outgoing
call ("md" package only) it is used as a signal to out-pulse the
address information when doing overlapped sending.
On an incoming call it is used as an event to indicate that an MF
digit string has been received. In this case, <inf-digits> are all
of the digits accumulated up to and including the digit delimiters
ST, ST', ST'', ST'''. Multiple sequences of digits ending with one
of the ST digits may be passed in a single "inf" event. (Note that
K0 is the same as KP, K1 is sometimes referred to as KP' etc.
Similarly S0 is the same as ST, S1 is the same as ST' and so on.
The value of <inf-digits> is a comma separated list of MF digits:
MF1, MF2, ..., MFn
where each of MFi will be one of the following MF digit symbols:
Table 11 MF Digit Symbols
-------------------------
| Symbol |MF digit |
| 0 | MF 0 |
| 1 | MF 1 |
| 2 | MF 2 |
| 3 | MF 3 |
| 4 | MF 4 |
| 5 | MF 5 |
| 6 | MF 6 |
| 7 | MF 7 |
| 8 | MF 8 |
| 9 | MF 9 |
| K0 | MF K0 or KP |
| K1 | MF K1 |
| K2 | MF K2 |
| S0 | MF S0 or ST |
| S1 | MF S1 or ST' |
| S2 | MF S2 or ST'' |
| S3 | MF S3 or ST'''|
--------------------------
Thus, an example signal or event might look like:
inf(k0, 5,5,5,1,2,3,4, s0)
An example where the inter-digit timer expired after the 5,5,5 would
appear as follows:
inf(k0, 5,5,5)
Operation Complete (oc ; x + -; all): The operation complete event is
generated when the gateway was asked to apply one or several signals
of type TO on the endpoint, and one or more of those signals
completed without being stopped by the detection of a requested or
persistent event such as setup. The completion report may carry as a
parameter the name of the signal that came to the end of its live
time, as in:
O: ms/oc(ms/sup)
or
O: bl/oc(bl/rg)
When the operation complete event is requested, it cannot be
parameterized with any event parameters.
Note that when requested at the same a signal for "sup" (out-pulsing
- a TO event), the operation complete event will indicate when out-
pulsing is complete.
Operation failure (of; x + -; all): In general, the operation
failure event may be generated when the endpoint was asked to apply
one or several signals of type TO on the endpoint, and one or more of
those signals failed prior to timing out. The completion report may
carry as a parameter the name of the signal that failed, as in:
O: ms/of(ms/sup)
or
O: bl/of(bl/rg)
When the operation failure event is requested, it cannot be
parameterized with any event parameters.
Operator ringback (orbk; x + -; MO): The description of the signaling
MF CAS signaling that results in this event is describe in the
appendix of TR-NPL-000258 [3]. In brief, it is normally a wink-on
signal which may or may not be followed by an MF tone. This event
will be generated when the operator service requests that the calling
party be alerted ("mo" package only).
Reverse make busy (rbz; P + -; MO): This event corresponds to a
"blocking" (off-hook) generated by the other end of the one-way
operator services trunk ("mo" package). It has the same semantics as
of the "bl" event in other packages.
Operator recall (rcl; - + BR; MO): This signal may be applied to
invoke operator recall, e.g., due to customer hook-flash to bring the
operator back.
Release call (rel; P,S + BR; BL,DT,MD,MO,MS,DO): A "rel" signal sent
by the Call Agent to the Media Gateway is a request to release all of
the resources associated with the telephony leg of the call. This
may also result in an off-hook signal being sent when appropriate.
As a result of an "rel" signal, the gateway will respond with an
"rcl" event, whenever the resources have been released. Releasing
resources associated with the telephony leg of the call does not
affect existing connections (network legs). It's up to the Call
Agent to send the appropriate delete connection commands in order to
release any network connections to that endpoint.
In the case of the FXS ("BL") package, the "rel" signal is used to
provide a tip-ground release for ground-start trunks. In the case of
loop-start trunks, requesting to play this signal has no effect.
The Media Gateway generates a "release call" event whenever a call is
released as a result of an on-hook event from an originating end of a
call (normal release) or due to abnormal event that resulted in
releasing the call. The event may be parameterized with one of the
following cause codes indicating the reason for the release:
Table 12 Release Reason Codes
-----------------------------------------------------------------
|Cause Code |Reason |
|-----------------------------------------------------------------
| 0 |Normal release |
| 44 |Requested channel/circuit not available |
| |(glare or incoming seizure detected during call |
| | setup) |
| 111 |Protocol/signaling error, unspecified (e.g. timeout) |
-----------------------------------------------------------------
Note that a "rel" event with reason code "0" indicating normal
release (due to an incoming on-hook) will only be "notified" by a
gateway where a call origination occurred. This behavior follows the
rule that when an originator releases the call, all resources may be
released. The corresponding event for on-hook on the terminating end
of a call is the "sus" event which only indicates hook-status and
does not result in any resources being released. It is always up to
the Call Agent to release the call (by sending the "rel" signal) for
the terminating end of a call.
For FXO ground-start case ("DO" package), the Media Gateway generates
a "release call" event whenever a call is released as a result of a
tip-ground release event from the far end.
Resume call (res ; P + BR; DT,MD,MS,MO): This indicates that the
called party resumed the call, i.e., the party went off-hook after a
previous suspend ("sus") but before the originating switch released
("rel") the trunk. The "sus" and "res" events/signals are used to
propagate on-hook and off-hook events without releasing the resources
associated with the call. In all but the operator services case
("MO" package), these events would normally be propagated from the
terminating to the originating end (i.e., requested as events from
the terminating end of the call and sent to the gateway as signals to
a gateway on the originating side of the call).
However, it is up to the Call Agent to decide whether it wants to do
"suspend"/"resume" processing. If it doesn't, when it receives a
"sup" event from the terminating end of the call it can simply go
ahead and tear down the call immediately (send "rel" and delete
connections to the endpoints on gateways at both originating and
terminating end of the call).
In the case of operator services and 911, "sus" and "res" are used to
pass off-hook and on-hook signals to the operator without releasing
any of the resources associated with the call.
Ringing (rg; P,S + TO; BL,DO): This signal is used for outgoing basic
trunks ("bl" package). See GR-506-CORE - LSSGR: SIGNALING, Section
14. The provisioning process may define the ringing cadence. It is
considered an error to try and ring if the trunk indicates off hook
and an error should consequently be returned when such attempts are
made (error code 401 - phone off hook).
In the case of the "DO" package, "rg" is defined as an event used to
indicate detection of ringing.
Release complete (rlc;P,S + BR; DO,DT,MD,MO,MS): The endpoint and
Call Agent use the release complete event/signal to confirm the call
has been released and the trunk is available for another call. For
FXO ground-start ("DO" package), this represents the release of the
tip-ground event from the PBX after the gateway goes on-hook.
Reorder tone (ro; - + TO; BL,DT,MD,MS): Reorder tone is a combination
of two AC tones with frequencies of 480 and 620 Hertz and levels of
-24 dBm each, to give a combined level of -21 dBm. The cadence for
reorder tone is 0.25 seconds on followed by 0.25 seconds off,
repeating continuously. See GR-506-CORE - LSSGR: SIGNALING, Section
17.2.7.
Ring back tone (rt; - + TO; BL,DT,MD,MS): Audible Ring Tone is a
combination of two AC tones with frequencies of 440 and 480 Hertz and
levels of -19 dBm each, to give a combined level of -16 dBm. In the
US the cadence for Audible Ring Tone is defined to be 2 seconds on
followed by 4 seconds off. The definition of the tone is defined by
the national characteristics of the Ring-back Tone, and MAY be
established via provisioning. See GR-506-CORE - LSSGR: SIGNALING,
Section 17.2.5.
Call Setup (sup ; P,S + TO; DO,DT,MD,MS,MO): The event/signal is used
both for outgoing and incoming call setups. Each will be described
separately in the following.
Outgoing call setup:
On an outgoing trunk, the "sup" signal is used to seize a trunk and
out-pulse digits. The "sup" signal is parameterized with up to four
parameters sup(<ct>, <ca>, <id>, <addr>), depending on the package.
The order of these parameters does not matter. The following table
indicates which ones are mandatory ("M"), optional ("O") or forbidden
("F") for the various packages.
Table 13 "sup" parameters.
------------------------------------
| Parameter | MS | DT | MO | MD | DO |
|------------------------------------|
| <ct> | F | F | F | M | F |
| <ca> | F | F | F | O | F |
| <id> | F | F | M | M | F |
| <addr> | M | M | M | O | M |
------------------------------------
The <ct> parameter is of the format ct(<ct-value>) where <ct-value>
indicates the CAS signaling type and can have one of two values "nda"
(North American Direct Access) for EANA and "nta" (North American
Tandem Access) for EAIN. The reason this parameter is needed in the
case of trunks that handle the "MD" packages is because the same
trunk can be used for both. The <addr> field contains the
destination number and when present will be on the form
addr(dig1, dig2, ..., dign)
The <id> field contains the identification of the caller and when
present will be of the form:
id(dig1, dig2, ..., dign)
The <ca> field contains the country address information and when
present will be of the form:
ca(dig1, dig2, ..., dign)
When present, the <addr> field contains the destination number and
will be of the form
addr(dig1, dig2, ..., dign)
where digi is an MF symbol as defined in table 11 in the case of
"MS", "MO", and "MD" packages and digi is a DTMF symbol (0-9,
*,#,A,B,C,D) in the case of the "DT" and "DO" packages.
The following table shows some interactions between the Media Gateway
(MG) and the Switched Circuit Network (SCN) for single stage
outpulsing applications ("DT", "MS" and "DO" packages):
Table 14 SCN Sequencing during Call Setup (single stage outpulsing)
------------------------------------------------------------------
|Interface Type |Setup | Interactions |
|------------------------------------------------------------------|
|wink start |sup(add(<addrvalue>)) |MG| off-hook -> |SCN|
| | |MG| <- wink |SCN|
| | |MG| <addrvalue> -> |SCN|
|------------------------------------------------------------------|
|Immediate Start|(sup(addr(<addrvalue>)) |MG| off-hook -> |SCN|
| or FXO) | |MG| <addrvalue> -> |SCN|
------------------------------------------------------------------
Call setup signal example for this case (MF signaling):
sup(addr(s0,5,5,5,1,2,3,4,k0))
The "MO" and "MD" packages involve multi-stage signaling and multiple
parameters. In the case of the "MD" package the following table
shows some of the interactions:
Table 15 SCN Sequencing during Call Setup (EANA and EAIN)
------------------------------------------------------------------
|Setup | Interactions |
|------------------------------------------------------------------|
| sup(ct(nda),addr(<addrvalue>), |MG| off-hook -> |SCN|
| id(<idvalue>)) |MG| <- wink |SCN|
| |MG| <idvalue> -> |SCN|
| |MG| <addrvalue> -> |SCN|
|------------------------------------------------------------------|
| sup(ct(nta), ca(<cavalue>), |MG| off-hook -> |SCN|
| addr(<addrvalue>), id(<idvalue>)) |MG| <- wink |SCN|
| |MG| <cavalue> -> |SCN|
| |MG| <- wink |SCN|
| |MG| <idvalue> -> |SCN|
| |MG| <addrvalue> -> |SCN|
|------------------------------------------------------------------|
| sup(ct(nta), ca(<cavalue>), |MG| off-hook -> |SCN|
| id(<idvalue>)) |MG| <- wink |SCN|
| |MG| <cavalue> -> |SCN|
| |MG| <- wink |SCN|
| |MG| <idvalue> -> |SCN|
------------------------------------------------------------------
The last example is an overlapped sending example where the address
value would be sent later using the "inf" signal.
An example setup:
sup(ct(nta),ca(k0,1,3,8,9,9,0,0,1,0,s0),id(k0,0,5,5,5,1,2,3,4,s0))
In all of the above cases, the "ans" event is an indication of off-
hook from the far end (the other end answered). However, in the case
of the operator service signaling (OSS) protocol of Feature Group D -
shown in the following table, off-hook from the operator is part of
the protocol (a request for the calling number) so that "ans" in this
case does not indicate that the operator answered (only that off-
hook/request for calling number was received).
Table 16 SCN Sequencing during Call Setup OSS Protocol ("MO" Package)
------------------------------------------------------------------
|Setup | Interactions |
|------------------------------------------------------------------|
| sup(ct(nda),addr(<addrvalue>), |MG| off-hook -> |SCN|
| id(<idvalue>)) |MG| <- wink |SCN|
| |MG| <- off-hook |SCN|
| |MG| <addrvalue> -> |SCN|
| |MG| <idvalue> -> |SCN|
------------------------------------------------------------------
Incoming Call Setup: A "sup" event is used to indicate when an
incoming call arrives (corresponding to the incoming off-hook event).
The event is provided without parameters.
Suspend call (sus; P + BR; DT,MD,MS,MO): Suspend ("sus") is an on-
hook event that is an indication that the called party went on-hook.
An on-hook event will be "notified" to a Call Agent as a "sus" event
for interfaces that use the "MS", "DT" and "MD" packages from an
endpoint at a terminating end of a call (as compared to a "rel" event
from the originating side). The "sus" event from the terminating
endpoint gives the Call Agent the option of doing "suspend/resume"
processing or to simply release the call.
The "sus" signal may be used to send an on-hook to the originating
party without releasing the resources associated with the telephony
leg of the call. The "rel" signal on the other hand would send an
on-hook and release the resources associated with the call.
Because of this "sus" can be followed by "res" (off-hook) and allow
the call to resume, while "rel" cannot be followed by "res" because
the call no longer exists.
For E911 ("MO" package), the operator is normally in control of
releasing the call so that, "sus" (on-hook), "res" (off-hook) and
"rcl" (flash-hook) can be used to pass user hook events to the
operator without releasing the call.
Start Wink (swk; x + - MD,MO):. An Call Agent can optionally request
the MG to notify it when the wink start signal occurs. Note that
wink start ("swk") cannot be applied by the Call Agent as a signal.
The occurrence of wink-start on an incoming trunk is a reflexive
action that does not require Call Agent involvement.
3.0. Hook-State Signals and Events
3.1. Overview of Approach
As mentioned in the introduction, a higher level view is taken for
on-hook and off-hook events for many of the CAS packages to make the
interface Q.931-like. This provides the advantage that:
* Similar call flows result as when dealing with Q.931-based
interfaces (e.g., PRI)
* It's more evident (for ease in debug) when looking at message as
to exactly what is going on without having to refer to previous
flows.
This does require that media gateways maintain some state but this is
a relatively small price to pay.
One example of this is the "sup" signal which involves sending off-
hook followed by digits as a high level signal. The "ans" event is
also used to represent off-hook but from the terminating end at the
point where the call is answered.
3.2. Suspend/Resume Processing
Other signals and events "sus" for suspend, "res" for resume and
"rel" for release are based on the concept that one end (the
originator) is in control of the call. If the controlling end goes
on-hook a "rel" is notified to the Call Agent, and results in a the
call being released. However, if the non-controlling (terminating)
end goes on-hook, a "sus" event occurs (instead of the "rel" event).
This gives the Call Agent the option of doing suspend/resume
processing.
If the Call Agent decides not to do suspend/resume processing, it can
simply send "rel" and delete connection commands to the endpoints
after it receives "sus" from the non-controlling (terminating) end of
the call.
On the other hand, if it decides to do suspend/resume processing, it
can start a timeout when it receives the "sus" event from the non-
controlling (terminating) end of the call and continue the call if it
receives a "res" (off-hook) event. It also has the option of
propagating the "sus" and "res" as signals back to the ingress
gateway and allow it an opportunity to release the call ("rel" event)
or not. In any case the use of "sus" and "res" signals give another
level of control over the "rel" signal which will not only send on-
hook but also release the resources associated with the telephony leg
of the call.
3.3. Control over Disconnect for E911
Note that for E911 (the "MO" package) is a special case in that the
operator (terminating end) is always the controlling end. The "sus"
and "res" signals are used to pass user hook state forward to the
operator. The "rel" event is passed back as a notify to the Call
Agent when on-hook is received from the operator indicating that the
Call should be released. If the "rel" is not received the call
should continue to stay up.
3.3. Release and Release Complete
The "rel" signal/event generally means on-hook but more that that it
also indicates "release of resources" for the telephony leg of the
call. If a Call Agent sends a "rel" signal instead of "sus" it is
requesting the call to be abandoned (i.e., "rel" cannot be followed
by "res").
The "rel" signal does not also imply that connections should be
deleted so that to completely release the call including connections
would require a DLCX in addition to (or conjunction with) the signal
"rel".
In addition to being a signal, "rel" can also be an event triggered
by either:
* An on-hook from the controlling end of the call, or
* Some abnormal event within the media gateway such that the
telephony leg of the call can no longer be maintained.
In any case, "rel" (release) is generally followed by an "rlc"
(release complete). The release complete signal/event indicates that
the trunk resources are now completely released and available for
another call. This is also an event state that can be audited as
indicated by the "S" in the column for that event (allowing the Call
Agent to check to see if that trunk is released and available).
Examples of the use of "rel" and "rlc":
* Call Agent sends a "rel" to release a trunk, resulting in an
outgoing off-hook being sent for that trunk. When the media
gateway receives the on-hook from the other end, it returns an
"rlc" event indicating that the trunk is released and available.
* The media gateway receives a on-hook from the trunk at the
controlling end of the call, resulting in a "rel" event being sent
to the Call Agent. The Call Agent then sends an "rlc" to the
media gateway, resulting in on-hook being sent in the opposite
direction.
* An "rel" event is sent to the Call Agent in the event of some
abnormal condition in which the media gateway is unable to sustain
the telephony leg of the call (e.g., glare condition). The Call
Agent sends an "rlc" to the gateway to complete the release of the
call. (note that "rlc may not correspond to on-hook but is
generally sent anyway in response to a "rel".)
* The Call Agent can send a "rel" (instead of "sus") signal to the
controlling (originating) end of the call to abandon the call.
The gateway will return with "rlc" when an off-hook has been
received from the other end and all the resources have been
released.
* A "rel" can be sent on one-way incoming trunk to release a block
("bl") sent earlier.
The "BL" (FXS) package is a simple line package, so does not have
these events (uses "hd", "hf", and "hu" as the only hook state
events).
The "DO" (FXO) package, however, does have "rel" and "rlc" because in
the ground-start case there is the ability to "release" the call as
result of a tip-ground release. The signal "rel" is used if the PBX
releases the call first (followed by S: hu from the call Agent to
complete the release). Alternatively, the Call Agent can send the S:
hu to initiate the release - followed by an "rlc" event from the
media gateway to Call Agent when the PBX does the tip ground release.
Although the loop-start trunks would not normally have this behavior
(only applies to ground-start), the media gateway should emulate the
behavior in the case of loop-start in order to allow the Call Agent a
common interface.
3.4. Blocking CAS Trunks
In addition to the above signals and events, there is the "bl"
signal/event which is used for blocking one-way trunks (does not work
for two way trunks) by providing a continuous off-hook.
3.5. Summary of Hook-State Events
The following summarizes the use of the various events that involve
off-hook and on-hook from call establishment to tear-down. This
applies mainly to "MS", "DT", "MD" and to a lesser extent the "DO"
package.
* The "sup" event represents off-hook origination.
* The "sup" signal with parameters provides off-hook with digit
outpulsing on the terminating side.
* Once outpulsing is completed, an "ans" event indicates off-hook
from the termination side (the called party has answered).
* The call agent can then send an "ans" signal (off-hook) to the
originating end to indicate to the caller that the called party
has answered.
* The Call Agent can send a "rel" to either end at any time to tear
down the call (e.g., to abort the call).
* The media gateway can send "rel" to indicate abnormal termination
of the call (with a reason as a parameter).
* However, under normal operation once a call is established, the
Call Agent can expect a "sus" (suspend) event from the termination
end to indicate that the caller went on-hook and a "res" if the
called party goes off-hook again before the Call Agent tears down
the call. The Call Agent can send these same signals to the
originating end to indicate off-hook and on-hook to the calling
party without tearing down the call.
* During normal operation, once the call is established, on-hook
from the calling party (origination side) would result in a "rel"
signal. The Call Agent would then normally send the "rel" signal
to the terminating end to terminate the call. "rel is normally
followed by "rlc" (e.g., media gateway indicates calling party on-
hook with "rel" and the Call Agent responds with "rlc", which
sends on on-hook back to the calling party to indicated release
complete.
The "MO" package is a bit different in that normally only the
terminating side (the operator) can release the call ("rel" event).
The "sus" and "res" are forward signals to the operator indicating
user hook-status.
4.0. Glare Handling
4.1. Glare on MF Bi-directional Wink-start Trunks
Gateways may have a configurable glare bit on a per-DS0 basis that
can be set to indicate whether the gateway is the controlling or
non-controlling "switch". However, in general, PBXs are either pre-
configured or can be configured to behave as non-controlling
switches. In this case if they see an off-hook that exceeds
allowable wink length, they will attach a receiver, go on-hook, and
await digits for a new call. Meanwhile the PBX will retry its
original call on another trunk.
If the gateway behaves like a controlling switch, when glare is
detected, the gateway will wait for up to some timeout value (default
value of 4 seconds) until the incoming off-hook changes to an on-hook
state at which time it will start out-pulsing in the normal manner.
If the timeout occurs before the state change to on-hook occurs, the
gateway will send a release event to the Call Agent (a "rel(44)"
event - cause code indicating glare).
When "rel(44)" is sent by the gateway, that is an indication to the
Call Agent that the call is in the process of being released and that
the Call Agent should give up on that trunk. However, the gateway
may not actually want to send the on-hook at that time in order to
avoid the possibility that the other end takes the on-hook as a wink.
Instead, it may start a second timer and wait some longer period of
time (e.g., 16 seconds or so) before releasing the trunk. If it
receives an on-hook prior the timeout, it completes the release by
going on-hook. If, on the other hand, the timer expires before the
other end goes on-hook, it will simply go on-hook and wait for the
other end to go on-hook. In any case, once both ends have returned
to the on-hook state, an "rlc" event is sent to the Call Agent.
4.2. Glare Handling - Basic PBX Trunks
In order to reduce the chances of glare, the gateway should try a
ringing pre-trip test prior to sending ringing on a basic ground
start trunk. If glare is detected on an outgoing seizure of a basic
PBX trunk, the request for ringing should be "Nacked" (error code 401
- phone off-hook) to the Call Agent.
5.0. Example Call Flows
5.1. PBX to PBX ("MS", "DT, and "BL" packages).
The following call flows involve a single Call Agent that handles
both sides of the call (i.e., the inter-Call-Agent signaling is
ignored). The components involved in the call are:
* The Call Agent (CA)
* The originating Media Gateway (GW-o) and
* The terminating Media Gateway (GW-t)
5.1.1. Call Setup Flows
The following describes some PBX to PBX call. The table gives an
overview of the initial part of the call flow with details to follow.
---------------------------------------------------------------------
| Steps | GW-o | CA | GW-t |
|---------------------------------------------------------------------|
| A1 | NTFY[seizure] -> |
| A2 | <- Ack |
| A3 | <- RQNT[request digits] |
| A4 | Ack -> |
| A5 | NTFY[digits] -> |
| A6 | <- Ack |
| B1 | <- CRCX [M:recvonly, LCO] |
| B2 | Ack[SDP1] -> |
| B3 | CRCX [M:sendrecv, LCO, SDP1] -> |
| B4 | <- Ack [SDP2] |
| B5 | <- MDCX [recvonly,SDP2] |
| B6 | Ack -> |
---------------------------------------------------------------------
Step A1 PBX seizure results in a notify to the Call Agent
indicating the start of a call setup:
NTFY 3001 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
X: 0123456789AF
O: ms/sup (or dt/sup)
In the case of the "BL" package (basic PBX) the interface looks
like a simplified line interface with the standard "hd" event for
off-hook:
NTFY 3001 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
X: 0123456789AF
O: bl/hd
Another alternative would have been to use an embedded request in the
RQNT that resulted in this notify and combine that request with step
A3. Example - "ms" package:
RQNT 2001 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
X: 0123456789AF
R: ms/sup(E(R(ms/inf, ms/rel))
Step 3 could also be eliminated by the use of "loop" mode e.g.:
RQNT 2001 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
X: 0123456789AF
Q:loop
R: ms/sup, ms/inf, ms/rel
This would result in both notifies occurring without requiring the
RQNT in step A3.
Step A2 The Call Agent sends an Ack:
200 3001 OK
Step A3 The Call Agent requests that digits be collected. The
approach used here depends on the type of PBX interface. For an MF
interface the Call Agent requests that information digits be
collected as follows:
RQNT 2001 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
X: 0123456789B0
R: ms/inf, ms/rel
The Call Agent also asks to be told if the trunk gets released
for some reason ("rel" event) in the process of call setup
(release event may be due to some signaling error for example).
For DTMF trunks (wink-start, immediate start and Basic PBX), the
request is based on a digit map so looks a bit different:
RQNT 2001 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
X: 0123456789B0
R: d/[0-9*#T](D), dt/rel (bl/hd in the case of Basic PBX)
D: (xxxxxxx | x.[T#])
S: dt/dl
Note: the request to signal dial-tone may or may not be here
depending on PBX interface requirement - bl/dl required for
Basic PBX; dt/dl for some Immediate Start interfaces.
Step A4 The gateway responds with an ack:
200 2001 OK
Step A5 Once the digits are collected the gateway notifies the call
agent. In the case of an MF interface, the resulting notify will
look like the following
NTFY 3002 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
X: 0123456789B0
O: ms/inf(k0,5,5,5,1,2,3,4,s0)
In the case of a DTMF interface (including Basic PBX), it will
look like the following:
NTFY 3002 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
X: 0123456789B0
O: d/5,d/5,d/5,d/1,d/2,d/3,d/4
Step A6 The Call Agent responds with an ack:
200 3002 OK
Step B1 The Call Agent now requests that a receive-only connection
be made.
CRCX 2002 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
C: A7453949499
L: a:PCMU,s:off,e:on
M: recvonly
X: 0123456789B1
R: ms/rel (or dt/rel or bl/hu).
Step B2 The Gateway acks with a connection ID and provides the SDP
information:
200 2002 OK
I: 23474FE
v=0
o=- A7453949499 0 IN IP4 128.96.41.1
s=-
c=IN IP4 128.96.41.1
t=0 0
m= audio 3456 RTP/AVP 0
Step B3 The Call Agent passes this SDP information to the
terminating gateway (GW-t) as part of the connection request:
CRCX 4001 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
C: A7453949499
X: 45375840
L: a:PCMU,s:off,e:on
M: sendrecv
v=0
o=- A7453949499 0 IN IP4 128.96.41.1
s=-
c=IN IP4 128.96.41.1
t=0 0
m=audio 3456 RTP/AVP 0
Note that the call setup on the terminating trunk can be done with
this CRCX, although in this call flow - it is shown later (step C1).
Step B4 The terminating gateway, responds with an ack and its SDP
information:
200 4001 OK
I: 34738A
v=0
o=- A7453949499 0 IN IP4 47.123.34.33
s=-
c=IN IP4 47.123.34.33
t=0 0
m= audio 3456 RTP/AVP 0
Step B5 Call Agent sends a modify connection request with
connection mode receive-only to the origination gateway and includes
the SDP information with the selected profile from the termination
gateway.
MDCX 2003 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
C: A7453949499
I: 34738A
M: recvonly
v=0
o=- A7453949499 0 IN IP4 47.123.34.33
s=-
c=IN IP4 47.123.34.33
t=0 0
m= audio 3456 RTP/AVP 0
Step B6 The Gateway Acks the modify connection request
200 2003 OK
The following table shows the remainder of the call flow to set up
the call except for Basic PBX (Basic PBX shown in) with details to
follow.
---------------------------------------------------------------------
| Steps | GW-o | CA | GW-t |
|---------------------------------------------------------------------|
| C1 | RQNT [S: ms/sup, R: ms/oc, ms/rel, ms/ans] ->|
| C2 | <- Ack |
| C3 | <- NTFY [O:ms/oc(ms/sup)]|
| C4 | Ack -> |
| C5 | <- NTFY [O: ms/ans] |
| C6 | Ack -> |
| C7 | <- MDCX [M:sendrecv, S: ms/ans, R: ms/rel] |
| C8 | Ack -> |
| C9 | RQNT[R: ms/sus] -> |
| C10 | <- Ack |
---------------------------------------------------------------------
Step C1 The Call Agent does a setup request to the terminating
gateway The setup request for an MF PBX interface (wink start or
immediate start) will be the following:
RQNT 4002 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
X: 45375841
Q: loop
S: ms/sup(addr(ko,5,5,5,1,2,3,4,s0))
R: ms/oc, ms/rel, ms/ans
Note that the result of the "sup" signal is the following
sequence on the interface to the PBX:
* off-hook -> PBX
* wink -> PBX (for wink-start trunks; for immediate start this
part of the sequence does is not included)
* Digits sent to PBX
For DTMF PBX interface (except Basic PBX), the only difference is
that the MF start and end delimiters (k0 and s0) are not
included:
RQNT 4002 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
X: 45375841
Q: loop
S: dt/sup(addr(5,5,5,1,2,3,4))
R: dt/oc, dt/rel, dt/ans
Basic PBX requires ringing and ring-back instead i.e.:
RQNT 4002 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
X: 45375841
Q: loop
S: bl/rg,bl/rt@34738A
R: bl/oc,bl/hd
In this case ringback will come from the gateway and will start
immediately with the signal request for rt@connectionID. It will
end as soon as an event occurs (off-hook representing answer
event) In the case of other PBX's, the ringback tone comes from
the PBX so does not have to be generated by the gateway.
Note that these requests could be done as easily at the same time
as the connection request (B3) saving some post-dial delay time.
Step C2 The gateway responds with an ack:
200 4002 OK
Step C3 Except for the basic PBX, case (where digits are not
outpulsed) when the digits have completed being sent out, the gateway
will notify the fact by indicate that the operation is complete.
NTFY 1001 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
X: 45375841
O: ms/oc(ms/sup) (or dt/oc(dt/sup))
Step C4 The Call Agent acks the notify
200 1001 OK
In the case of the BL package, steps C3 and C4 will not exist.
Step C5 When an answer is obtained from the other end (off-hook
from the PBX), the gateway sends a notify to indicate:
NTFY 1002 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
X: 45375841
O: ms/ans (or dt/ans or bl/hd)
Step C6 The Call Agent acks
200 1002 OK
Step C7 The Call Agent now sends a request to make the connection
full duplex and indicates that the other end has answered the phone.
MDCX 2004 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
C: A7453949499
X: 45375842
I: 34738A
M: sendrecv
S: ms/ans ( or dt/ans but S: not included in the case where the
originating gateway uses the BL package)
Step C8 The Gateway acks the request
200 2004 OK
Step C9 The Call Agent sends a notification request to be told
when the trunk to be released.
RQNT 4003 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
X: 45375842
R: ms/rel,ms/sus (or R: dt/rel,dt/sus or R: bl/hu)
Step C10 The gateway acks the request
200 4003 OK
The call is now setup.
5.1.2. Call Tear-Down
Two cases are included here, one where the origination end initiates
the release (section 5.1.2.1) and one where the termination end
initiates the release (section 5.1.2.2).
5.1.2.1. Origination End Initiates the Release
The following call flow shows an example where the origination end
initiates the release for the "MS" package (similar for "DT"
Package).
--------------------------------------------------------------------
| Steps | GW-o | CA | GW-t |
|-------------------------------------------------------------------- |
| A1 | NTFY[O: ms/rel] -> |
| A2 | <- Ack |
| A3 | RQNT [S: ms/rel, R: ms/rlc] -> |
| A4 | <- Ack |
| A5 | <- NTFY [O: ms/rlc] |
| A6 | Ack -> |
| A7 | <- DLCX [S: ms/rlc, R: ms/sup] |
| A8 | Ack [perf info] -> |
| A9 | DLCX [R: ms/sup]-> |
| A10 | <- Ack [perf info] |
---------------------------------------------------------------------
The same call flow for the "BL" package is shown below
---------------------------------------------------------------------
| Steps | GW-o | CA | GW-t |
|---------------------------------------------------------------------|
| A1 | NTFY[O: bl/hu] -> |
| A2 | <- Ack |
| A3 | RQNT [S: bl/dl, R: bl/hu] -> |
| A4 | <- Ack |
| A5 | <- NTFY [O: bl/hu] |
| A6 | Ack -> |
| A7 | <- DLCX [R: bl/hd] |
| A8 | Ack [perf info] -> |
| A9 | DLCX [R: bl/hd]-> |
| A10 | <- Ack [perf info] |
---------------------------------------------------------------------
Step A1 The originating user goes on-hook resulting in a Notify
from the gateway to indicate that the trunk is being released (reason
indicating normal release)
NTFY 3005 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
X: 45375842
O: ms/rel(0) (or dt/rel(0) or bl/hu)
Step A2 The Call Agent Acks the Notify
200 3005 OK
Step A3 The Call Agent sends a request to release the trunk. (For
all but Basic PBX.)
RQNT 4004 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
X: 45375843
S: ms/rel (or dt/rel)
R: ms/rlc (or dt/rlc)
For the Basic PBX ("BL" package), dial-tone is played
RQNT 4004 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
X: 45375843
S: bl/dl
R: bl/hu
Step A4 The Gateways acks the request
200 4004 OK
Step A5 The other end releases the call by going on-hook and a
Notify is sent to the Call Agent to indicate that release is
complete.
NTFY 1004 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
X: 45375843
O: ms/rlc (or dt/rlc)
In the case of Basic PBX, this is:
NTFY 1004 ds/ds1-5/3@gw-o.whatever.net MGCP 1.0
X: 45375843
O: bl/hu
Step A6 The Call Agent returns an Ack
200 1004 OK
Step A7 The Call Agent sends a delete connection to the originating
gateway with a request to do a release complete (which results in
sending on-hook to the PBX).
DLCX 4005 ds/ds1-5/3@gw-o.whatever.net MGCP 1.0
X: 45375844
I: 34738A
S: ms/rlc (or dt/rlc)
R: ms/sup (or dt/sup)
Or in the case of Basic PBX ("BL" package):
DLCX 4005 ds/ds1-5/3@gw-o.whatever.net MGCP 1.0
X: 45375844
I: 34738A
R: bl/hd
Step A8 The Gateway Acks and provides performance information.
250 4005 OK
P: PS=1245, OS=62345, PR=0, OR=0, PL=0, JI=0, LA=48
Step A9 The Call Agent sends a DLCX to the terminating gateway.
DLCX 2004 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
X: 0123456789B3
I: 23474FE
R: ms/sup (or dt/sup or bl/hd)
Step A10 The gateway acks with performance information
250 2004 OK
P: PS=1245, OS=62345, PR=0, OR=0, PL=0, JI=0, LA=48
5.1.2.2. Termination End Initiates the Release
The following call flow gives an example of the terminating end
releasing a call for all but Basic PBX ("MS" package - "DT" package
is similar).
---------------------------------------------------------------------
| Steps | GW-o | CA | GW-t |
|---------------------------------------------------------------------|
| A1 | <- NTFY[O: ms/sus] |
| A2 | Ack -> |
| A3 | <- RQNT [S: ms/sus, R: ms/rel ] |
| A4 | Ack -> |
| A5 | RQNT [R: ms/res] -> |
| A6 | <- Ack |
| A7 | NTFY [O: ms/rel] -> |
| A8 | <- Ack |
| A9 | DLCX [S: ms/rel, R: ms/rlc] -> |
| A10 | <- Ack [perf info] |
| A11 | <- Notify [O: ms/rlc] |
| A12 | Ack -> |
| A13 | <- DLCX [S: ms/rlc, R: ms/sup ] |
| A14 | Ack [perf info] -> |
---------------------------------------------------------------------
The following shows the same call flow but for Basic PBX. There is
no equivalent to steps A3-A6 and A11-A12 - so these are not included.
---------------------------------------------------------------------
| Steps | GW-o | CA | GW-t |
|---------------------------------------------------------------------|
| A1 | <- NTFY[O: bl/hu] |
| A2 | Ack -> |
| A7 | NTFY [O: bl/hu] -> |
| A8 | <- Ack |
| A9 | DLCX [R: bl/hd] -> |
| A10 | <- Ack [perf info] |
| A13 | <- DLCX [bl/hd] |
| A14 | Ack [perf info] -> |
---------------------------------------------------------------------
Step A1 An on-hook is received from the PBX. In the case of all
but the "BL" package, this results in a notify with event "sus" for
suspend.
Step A2 The Call Agent returns an acknowledge
The Call Agent starts a timer at this point (typically 10
seconds). If an off-hook is received from the PBX connected to
GW-t before the origination side releases, the call is continued
(this would appear as a "res" event or "hd" in the case of Basic
PBX interface). If the origination side goes on-hook or the
timer expires, then the call is torn down.
Note that for Basic PBX (the "BL" package), steps A3 - A6 are
missing (these steps do not exist for basic PBX).
Step A3 A "sus" signal is sent to the originating side resulting in
a on-hook being sent to the originating PBX.
Step A4 GW-o acks the request.
Step A5 The Call Agent sends a request to see off-hook or resume
("res") events.
Note: this depends on whether the Call Agent wants to do
suspend/resume processing. If not, the Call Agent may simply send
"rel" along with DLCX to both ends.
Step A6 GW-t acks the request.
Step A7 An on-hook is received from the originating PBX resulting
in a notify from GW-o with event "rel" ("hu" for Basic PBX
interface).
Step A8 The Call Agent "acks"
Step A9 A delete connection is sent to the terminating gateway with
signal "rel" which results in on-hook being sent to the terminating
PBX (except for basic PBX - where there is no such signal)
Step A10 GW-t acks the DLCX and provides performance information
Steps A11 and A12 do not exist for the basic PBX case.
Step A11 GW-t returns an "rlc" event
Step A12 The Call Agent "acks" the notify
Step A13 A delete connection is sent to the originating side (with
signal "rlc" except in the case of the "BL" package).
Step A14 GW-o returns an "ack" with performance information.
5.2. Example Call Flows - "DO" package
5.2.1. Call Setup Flows
The following describes some PBX to PBX call. The table gives an
overview of the initial part of the call flow with details to follow.
---------------------------------------------------------------------
| Steps | GW-o | CA | GW-t |
|---------------------------------------------------------------------|
| A1 | NTFY[O: do/rg] -> |
| A2 | <- Ack |
| B1 | <- CRCX [S: do/hd, R: do/rel, M:recvonly, LCO] |
| B2 | Ack[SDP1] -> |
| B3 | CRCX [M:sendrecv, LCO, SDP1] -> |
| B4 | <- Ack [SDP2] |
| B5 | <- MDCX [recvonly,SDP2] |
| B6 | Ack -> |
| C1 | RQNT [S: do/sup, R: do/oc] -> |
| C2 | <- Ack |
| C3 | <- NTFY [O:do/oc(do/sup)]|
| C4 | Ack -> |
| C5 | <- MDCX [M:sendrecv, R: do/rel] |
| C6 | Ack -> |
| C7 | RQNT[R: do/rel] -> |
| C8 | <- Ack |
---------------------------------------------------------------------
Step A1 PBX rings results in a notify to the Call Agent indicating
the start of a call setup:
NTFY 3001 aaln/0@gw-o.whatever.net MGCP 1.0
X: 0123456789AF
O: do/rg
Step A2 The Call Agent sends an Ack:
Step B1 The Call Agent now requests that a receive-only connection
be made.
If the endpoint is running FXO ground-start, the call would also
request detection of disconnect supervision from the PBX (R:
do/rel) and should send an off-hook (S: do/hd) in response to
ringing.
Step B2 The Gateway acks with a connection ID and provides the SDP
information.
Step B3 The Call Agent passes this SDP information to the
terminating gateway (GW-t) as part of the connection request.
Step B4 The terminating gateway, responds with an ack and its SDP
information.
Step B5 Call Agent sends a modify connection request with
connection mode receive-only to the origination gateway and includes
the SDP information with the selected profile from the termination
gateway.
Step B6 The Gateway Acks the modify connection request
Step C1 The Call Agent does a setup request to the terminating
gateway The setup request will be the following:
RQNT 4002 aaln/0@gw-t.whatever.net MGCP 1.0
X: 45375841
S: do/sup(addr(5,5,5,1,2,3,4))
R: do/oc
Note that the result of the "sup" signal is the following
sequence on the interface to the PBX:
* off-hook -> PBX
* tip-ground <- PBX (for loop-start this step does not apply)
* digits sent to PBX
Step C2 The gateway responds with an ack:
200 4002 OK
Step C3 When the digits have been completely sent out, the gateway
will notify the fact by indicate that the operation is complete.
NTFY 1001 aaln/0@gw-t.whatever.net MGCP 1.0
X: 45375841
O: do/oc(do/sup)
Step C4 The Call Agent acks the notify
200 1001 OK
Step C5 The Call Agent now sends a request to make the connection
full duplex and indicates that the other end has answered the phone.
If the endpoint is running FXO ground-start, the call would also
requests detection of disconnect supervision from the PBX
(R:do/rel)
Step C6 The Gateway acks the request
Step C7 If the endpoint is running FXO ground-start, the Call Agent
sends a notification request to be told when the trunk to be
released (R: do/rel). This step and step C8 are not needed if the
endpoint is running FXO loop-start.
Step C8 The gateway acks the request and the call is now setup.
5.2.2. Call Tear-Down
If the endpoint is running FXO loop-start, the PBX cannot
initiate call release. In this case, call release is always
initiated by the Media Gateway by going onhook. Disconnect
supervision from the PBX is provided only for FXO ground-start.
However, it does not matter whether the origination end or the
termination end initiates the release. The call flows for either
case are the same. Therefore, only the case where the origination
end initiates the release is illustrated in this section.
---------------------------------------------------------------------
| Steps | GW-o | CA | GW-t |
|---------------------------------------------------------------------|
| A1 | NTFY[O: do/rel] -> |
| A2 | <- Ack |
| A3 | RQNT [S: do/hu, R: do/rlc] -> |
| A4 | <- Ack |
| A5 | <- NTFY [O: do/rlc] |
| A6 | Ack -> |
| A7 | <- DLCX [S: hu, R: rg] |
| A8 | Ack [perf info] -> |
| A9 | DLCX [R: do/rg]-> |
| A10 | <- Ack [perf info] |
---------------------------------------------------------------------
Step A1 The originating PBX goes on-hook resulting in a Notify from
the gateway to indicate that the trunk is being released (reason
indicating normal release).
NTFY 3005 aaln/0@gw-o.whatever.net MGCP 1.0
X: 45375842
O: do/rel(0)
Step A2 The Call Agent Acks the Notify
200 3005 OK
Step A3 The Call Agent sends a request to release the trunk.
Step A4 The Gateways acks the request
Step A5 PBX at the terminating end releases the call by releasing
tip-ground and a Notify is then sent to the Call Agent to indicate
that release is complete.
Note that there is no ground signal in case of loop-start.
However, this NTFY message is still generated as soon as hu
signal is applied.
Step A6 The Call Agent returns an Ack
Step A7 The Call Agent sends a delete connection to the originating
gateway with a request to go onhook.
Step A8 The Gateway Acks and provides performance information.
Step A9 The Call Agent sends a DLCX to the terminating gateway.
Step A10 The gateway acks with performance information
5.3. Example Call Setup - "MD" Package
The following describes Feature Group D call setup using the "MD"
package. The table gives an overview of the initial part of the call
flow with details to follow.
---------------------------------------------------------------------
| Steps | GW-o | CA | GW-t |
|---------------------------------------------------------------------|
| A1 | NTFY[O:md/sup] -> |
| A2 | <- Ack |
| A3 | NTFY[O:md/inf(<id>)] -> |
| A4 | <- Ack |
| A5 | NTFY[O:md/inf(<addr>)] -> |
| A6 | <- Ack |
| B1 | <- CRCX [M:recvonly, LCO, R: md/rel] |
| B2 | Ack[SDP1] -> |
| B3 | CRCX [M:sendrecv, LCO, SDP1] -> |
| B4 | <- Ack [SDP2] |
| B5 | <- MDCX [recvonly,SDP2] |
| B6 | Ack -> |
---------------------------------------------------------------------
The assumption is that prior to the initial "notify", the Call Agent
has sent a request to be informed of "sup" and "inf" events using
quarantine handling "Q: loop".
Step A1 Trunk seizure results in a notify to the Call Agent
indicating the start of a call setup:
NTFY 3001 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
X: 0123456789B0
O: md/sup
Step A2 The Call Agent sends an Ack.
Step A3 Once the digits for the identification field are collected
the gateway notifies the call agent:
NTFY 3002 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
X: 0123456789B0
O: md/inf(k0,0,0,4,0,8,5,5,5,1,2,3,4,s0)
Step A4 The Call Agent responds with an ack.
Step A5 When the digits are collected for the address field,
another notify is sent:
NTFY 3003 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
X: 0123456789B0
O: md/inf(k0,5,1,2,5,5,5,4,5,6,7,s0)
Step A6 The Call Agent "acks"
Step B1 Create connection - receive only:
CRCX 2002 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
C: A3C47F21456789F1
L: p:10, a:PCMU
M: sendrecv
X: 0123456789B1
R: md/rel
Step B2 The Gateway "acks" the request and provides connection ID
and SDP information.
Step B3 The Call Agent passes this SDP information to the
terminating gateway (GW-t) as part of the connection request.
Step B4 The terminating gateway, responds with an ack and its SDP
information.
Step B5 Call Agent sends a modify connection request with
connection mode receive-only to the origination gateway and includes
the SDP information with the selected profile from the termination
gateway.
Step B6 The Gateway Acks the modify connection request.
In the case of EAIN signaling there is some additional information
provided so that this initial part of the call setup looks slightly
different:
---------------------------------------------------------------------
| Steps | GW-o | CA | GW-t |
|---------------------------------------------------------------------|
| A1 | NTFY[O:md/sup] -> |
| A2 | <- Ack |
| A3 | NTFY[O:md/inf(<ca>)] -> |
| A4 | <- Ack |
| A5 | <- RQNT[S:md/cwk, R:md/inf,md/rel] |
| A6 | <- Ack |
| A7 | NTFY[O:md/inf(<id>)] -> |
| A8 | <- Ack |
| A9 | NTFY[O:md/inf(<addr>)] -> |
| A10 | <- Ack |
| B1 | <- CRCX [M:recvonly, LCO, R: md/rel] |
| B2 | Ack[SDP1] -> |
| B3 | CRCX [M:sendrecv, LCO, SDP1] -> |
| B4 | <- Ack [SDP2] |
| B5 | <- MDCX [recvonly,SDP2] |
| B6 | Ack -> |
---------------------------------------------------------------------
The assumption is that prior to the initial "notify", the Call Agent
has sent a request to be informed of "sup" and "inf" events using
quarantine handling "Q: loop".
Step A1 Trunk seizure results in a notify to the Call Agent
indicating the start of a call setup:
NTFY 3001 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
X: 0123456789B0
O: md/sup
Step A2 The Call Agent sends an Ack
Step A3 The initial digit string contains the country address
field:
NTFY 3002 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
X: 0123456789B0
O: md/inf(k0,1,3,8,9,9,0,0,1,9,s0)
Step A4 The Call Agent responds with an ack
Step A5 The Call Agent does processing on the country address field
and sends a request to initiate further input (sends a continue
wink):
RQNT 2002 ds/*@mgw45.whatever.net MGCP 1.0
X: 0123456789B1
Q: loop
R: md/inf,md/rel
S: md/cwk
Step A6 The Gateway "acks" the request.
Step A7 Once the digits for the identification field are collected
the gateway notifies the call agent:
NTFY 3003 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
X: 0123456789B0
O: md/inf(k0,0,0,4,0,8,5,5,5,1,2,3,4,s0)
Step A8 The Call Agent responds with an ack
Step A9 When the digits are collected for the address field,
another notify is sent:
NTFY 3004 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
X: 0123456789B0
O: md/inf(k0,5,1,2,5,5,5,4,5,6,7,s0)
Step A10 The Call Agent "acks"
Step B1 Create connection - receive only:
CRCX 2002 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
C: A3C47F21456789F1
L: p:10, a:PCMU
M: sendrecv
X: 0123456789B1
R: md/rel
Step B2 The Gateway "acks" the request and provides connection ID
and SDP information
Step B3 The Call Agent passes this SDP information to the
terminating gateway (GW-t) as part of the connection request.
Step B4 The terminating gateway, responds with an ack and its SDP
information
Step B5 Call Agent sends a modify connection request with
connection mode receive-only to the origination gateway and includes
the SDP information with the selected profile from the termination
gateway.
Step B6 The Gateway Acks the modify connection request
The following table shows the remainder of the call flow to set up
the call for FGD EANA.
---------------------------------------------------------------------
| Steps | GW-o | CA | GW-t |
|---------------------------------------------------------------------|
| C1 | RQNT [S:sup, R:md/swk,md/oc, md/rel,md/awk, md/ans] ->|
| C2 | <- Ack |
| C3 | <- NTFY [O:md/swk)] |
| C4 | Ack -> |
| C5 | <- NTFY [O:md/oc(md/sup)]|
| C6 | Ack -> |
| C7 | <- NTFY [O:md/awk)] |
| C8 | Ack -> |
| C9 | <- RQNT[S:md/awk] |
| C10 | Ack -> |
| C11 | <- NTFY [O: md/ans] |
| C12 | Ack -> |
| C13 | <- MDCX [M:sendrecv, S: md/ans, R: md/rel] |
| C14 | Ack -> |
| C15 | RQNT [R: md/sus, md/rel] -> |
| C16 | <- Ack |
---------------------------------------------------------------------
Step C1 The Call Agent does a setup request to the terminating
gateway The setup request for an MF EANA FGD interface will be the
following:
RQNT 2001 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
X: 45375841
Q: loop
S:
md/sup(ct(nda),addr(k0,5,5,5,5,2,2,1,2,3,4,s0),id(k0,0,5,5,5,1,
2,3,4,s2))
R: md/swk,md/oc,md/rel,md/awk,md/ans
Note that the result of the "sup" signal is the following
sequence on the interface to the PBX:
* off-hook -> SCN
* wink <- SCN
* caller ID digits sent to SCN
* address digits sent to SCN
Step C2 The gateway responds with an ack
Step C3 "Notify" the CA that the start of signaling has occurred
(incoming wink start has occurred) i.e.:
NTFY 3000 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
X: 0123456789B0
O: md/swk
Step C4 The Call Agent "acks".
Step C5 "Notify" that out-pulsing is complete:
NTFY 3001 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
X: 0123456789B0
O: md/oc(md/sup)
Step C6 The Call Agent "acks".
Step C7 "Notify" that the acknowledgement wink has been received:
NTFY 3002 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
X: 0123456789B0
O: md/awk
Step C8 The Call Agent "acks".
Step C9 The acknowledge wink is passed to the originating gateway:
RQNT 2001 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
X: 45375842
S: md/awk
R: md/rel
Step C10 GW-o "acks".
Step C11 "Notify" off-hook event (the person at the other end has
answered):
NTFY 3003 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
X: 0123456789B0
O: md/ans
Step C12 The Call Agent "acks".
Step C13 The Call Agent now sends a request to make the connection
full duplex and indicates that the other end has answered the phone
(S: ans sent)
Step C14 The Gateway acks the request
In the case of FGD EAIN, there is an additional digits string
(country address and/or carrier access code that has to be
included so that step C1 looks like the following in a case where
there is no overlapped sending:
RQNT 2001 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
X: 45375841
Q: loop
S:md/sup(ct(nta),ca(k0,1,3,8,9,9,0,0,1,0,s0),id(k0,
0,5,5,5,1,2,3,4,s0),addr(ko,0,1,1,3,8,1,2,3,4,7,6,5,s0))
R: md/swk,md/oc,md/rel,md/awk,md/ans
If overlapped sending is done, only the country address and
caller ID digit strings are sent out in step C1:
RQNT 2001 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
X: 45375841
Q: loop
S:md/sup(ct(nta),ca(k0,1,3,8,9,9,0,0,1,0,s0),id(k0,0,
5,5,5,1,2,3,4,s0))
R: md/swk,md/oc,md/rel,md/ans
Then after these digits go out indicated by event "oc(sup)" in
step C5, and as soon as the Call Agent has the address
information, it sends it out using the "inf" signal:
RQNT 2002 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
X: 0123456789B1
Q: loop
R: md/oc,md/rel,md/awk,md/ans
S: md/inf(ko,0,1,1,3,8,1,2,3,4,7,6,5,s0)
The Call Agent will then get a further "md/oc(md/sup)" event when
these digits have gone out.
Step C15 The Call Agent requests to be told of on-hook ("sus")
events
or abnormal release ("rel") events.
Step C16 The gateway "acks" the request.
5.4. Example Call Setup - "MO" Package
The following describes Feature Group D operator services signaling
call setup (911 call) using the "MO" package. The table gives an
overview of the initial part of the call flow with details to follow.
In this case GW-o is a residential gateway using the line package and
GW-t connects to the E911 tandem.
---------------------------------------------------------------------
| Steps | GW-o | CA | GW-t |
|---------------------------------------------------------------------|
| A1 | NTFY[O:hd] -> |
| A2 | <- Ack |
| A3 | <- RQNT S: dl, R: [0-9*#T](D) |
| A4 | Ack -> |
| A5 | NTFY[O: 9,1,1] -> |
| A6 | <- Ack |
| B1 | <- CRCX [M:recvonly, R: hu] |
| B2 | Ack[SDP1] -> |
| B3 | CRCX [M:sendrecv, LCO, SDP1, S: mo/sup] -> |
| B4 | <- Ack [SDP2] |
| B5 | <- NTFY [O: oc(sup)] |
| B6 | Ack -> |
| B5 | <- MDCX [sendrecv,SDP2] |
| B6 | Ack -> |
---------------------------------------------------------------------
Note: the originating side in this case is a line-side gateway.
Step A1 The user goes off-hook:
NTFY 3001 aaln/1@gw-o.whatever.net MGCP 1.0
X: 0123456789AF
O: l/hd
Step A2 The Call Agent sends an Ack:
200 3001 OK
Step A3 The Call Agent sends dial-tone and requests that digits be
collected:
RQNT 2001 aaln/1@gw-o.whatever.net MGCP 1.0
X: 0123456789B0
S: l/dl
R: d/[0-9#*T](D), hu
Step A4 The gateway responds with an ack:
200 2001 OK
Step A5 Once the digits are collected the gateway notifies the Call
Agent. In this case, it is a 911 call
NTFY 3002 aaln/1@gw-o.whatever.net MGCP 1.0
X: 0123456789B0
O: d/9,d/1,d/1
Step A6 The Call Agent responds with an ack:
200 3002 OK
Step B1 The Call Agent now requests that a receive-only connection
be made.
CRCX 2002 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
C: A7453949499
L: a:PCMU,s:off,e:on
M: recvonly
X: 0123456789B1
R: l/hu.
Step B2 The Gateway acks with a connection ID and provides the SDP
information:
200 2002 OK
I: 23474FE
v=0
o=- A7453949499 0 IN IP4 128.96.41.1
s=-
c=IN IP4 128.96.41.1
t=0 0
m= audio 3456 RTP/AVP 0
Step B3 The Call Agent passes this SDP information to the
terminating gateway (GW-t) as part of the connection request and does
a call setup request at the same time:
CRCX 4001 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
C: A7453949499
X: 45375840
L: a:PCMU,s:off,e:on
M: sendrecv
Q: loop
R: oc, rel, orbk
S: sup(addr(k0,9,1,1,s2),id(k0,0,8,3,4,5,6,7,8,s0))
v=0
o=- A7453949499 0 IN IP4 128.96.41.1
s=-
c=IN IP4 128.96.41.1
t=0 0
m=audio 3456 RTP/AVP 0
As a result of this request, the following signaling interactions
will occur between GW-t and the Switched Circuit Network (SCN - in
this case, the E911 tandem):
* Off-hook -> SCN
* Wink <- SCN
* k0,9,1,1,s2 -> SCN
* Off-hook <- SCN
* k0,0,8,3,4,5,6,7,8,s0
Note that off-hook from the SCN is part of the protocol (a
request for the caller ID) and does not provide an indication of
whether the operator answered or not.
Step B4 The terminating gateway, responds with an ack and its SDP
information:
200 4001 OK
I: 34738A
v=0
o=- A7453949499 0 IN IP4 47.123.34.33
s=-
c=IN IP4 47.123.34.33
t=0 0
m= audio 3456 RTP/AVP 0
Step B5 The Call Agent will get a further notify when outpulsing of
all of the digits is complete.
NTFY 3003 aaln/1@gw-o.whatever.net MGCP 1.0
X: 45375840
O: oc(sup)
Step B6 The Call Agent returns an "ack"
200 3003 OK
Step B7 Call Agent sends a modify connection request with
connection mode receive-only to the origination gateway and includes
the SDP information with the selected profile from the termination
gateway.
MDCX 2003 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
C: A7453949499
I: 34738A
M: sendrecv
v=0
o=- A7453949499 0 IN IP4 47.123.34.33
s=-
c=IN IP4 47.123.34.33
t=0 0
m= audio 3456 RTP/AVP 0
Step B8 The Gateway Acks the modify connection request
200 2003 OK
The call is now established between the user and the operator.
Acknowledgements
The source for some these packages are Flemming Andreasen, Wai-Tak
Siu - Cisco Systems, and Don Stanwyck - IP Unity. Special thanks to
Joe Clark, Telcordia Technologies for his CAS interface expertise.
Also thanks to all the reviewers for all their comments, including
but not limited to the following people: Charles Eckel, Cisco
Systems; Jerry Kamitses, Sonus Networks.
References
[1] Arango, M., Dugan, A., Elliott, I., Huitema, C. and S. Pickett,
"Media Gateway Control Protocol (MGCP) Version 1.0", RFC 2705,
October 1999.
[2] Handley, M. and V. Jacobson, "SDP: Session Description Protocol",
RFC 2327, April 1998.
[3] Bellcore, Compatibility Information for Feature Group D Switched
Access Service, TR-NPL-000258, Issue 1, October 1985.
[4] Bellcore, Interoffice LATA Switching Systems Generic Requirements
(LSSGR): Verification Connections (25-05-0903), TR-TSY-000531,
Issue 2, July 1987.
[5] Bellcore, LSSGR: Signaling for Analog Interfaces, GR-506-CORE,
Issue 1, June 1996.
[6] PacketCableTM PSTN Gateway Call Signaling Protocol Specification,
Pkt-SP-TGCP-I01-991201
Author's Address
Bill Foster
170 West Tasman Dr
San Jose, CA, 95134
Phone: 408-527-8791
EMail: bfoster@cisco.com
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